He was behind the plate to see Matt Harvey return to dominant form in Saturday’s 4-2 victory over the Cubs to open the series.

He received Yoenis Cespedes’ superb throw from left to nail Starlin Castro at the plate in the fifth to keep the game tied at 1-1.

And then he did something he has been trying to do since arriving at Citi Field: Hit one to the apple in center, which he finally accomplished in the most important game of his career, a bomb in the sixth inning to give the Mets a key insurance run.

“It was a great night overall,” d’Arnaud said. “I don’t know how much better it could have gone.”

He knew early on it might be a special night, even before he stepped on the field.

“The first two pitches from Matt were hard and exactly where we wanted them,” d’Arnaud said. “That was in the bullpen. And he just brought that out to the mound.”

They were pitches he didn’t see from Harvey during his shaky outing in Game 3 of the NLDS against the Dodgers, when he surrendered three runs in five innings and relied on a rare offensive outburst from his teammates.

And when Harvey finally did get into trouble, d’Arnaud was confident Cespedes had plenty of arm to get Castro, who ill-advisedly was sent home on a Javier Baez single to left in the fifth.

“I’ve seen Cespedes’ arm for long enough now,” d’Arnaud said. “As soon as he got to the ball, I knew he could get him. It was just a matter of me being in the right spot.”

“D’Arnaud hit one in the apple,” Murphy said. “I’ve never seen that before. I’ve been here for like I don’t know [how long]. We’ve been in this stadium since 2009. I’ve never seen someone drop it in the apple like that. That was a great at bat. Let us extend the lead.”